Magnesium to be used as a raw material of a magnesium ion battery is an element present abundantly on the earth, and is a material having higher superiority as compared with lithium which is unstable in price and supply amount or the like. In addition, since the magnesium ion battery is cheap and safe, as well as has high energy density, it has been drawn attention as a post-lithium ion battery.
As a negative electrode of the magnesium ion battery, usually metal magnesium is used. However, since metal magnesium has high reducibility, in the case where said metal is used as a negative electrode, it reacts with an electrolytic solution to form a passive state film having low ion conductivity, at the electrode surface thereof. There has been well known that formation of this passive state film inhibits reversible dissolution and deposition of magnesium, which has been a problem on using metal magnesium as a negative electrode.
On the other hand, an electrolytic solution not forming the passive state film has also been known. For example, in PATENT LITERATURE 1 and NON PATENT LITERATURE 1, there has been reported that by using an electrolytic solution, where an electrolyte represented by the general formula Mg(ZR11R2mXn)2 (wherein z represents a boron or an aluminum; R1 and R2 represent a hydrocarbon group; X represents a bromine or a chlorine; and l+m+n is 4) is dissolved in tetrahydrofuran (THF), reversible dissolution and deposition of magnesium is possible.
Additionally, various reports have been made aiming at enhancing performance of the magnesium ion battery. For example, in PATENT LITERATURE 2, there has been reported that by using an electrolytic solution, where an aromatic Grignard's reagent represented by the general formula C6H5MgX (wherein X═Cl, Br) is dissolved in tetrahydrofuran (THF), low oxidation potential of the Grignard's reagent (RMgX, wherein R is an alkyl group), which conventionally has been said, can be improved.
In addition, in PATENT LITERATURE 3 and PATENT LITERATURE 4, there has been reported that by using the Grignard's reagent (RMgX) or a magnesium chloride (II) and an organometal compound (an alkylaluminum compound) in combination, to form a complex by making magnesium dimerized in the system, acid resistance of an electrolytic solution can be improved.
Still more, in NON PATENT LITERATURE 2, there has been referred to on progress of reversible dissolution and deposition of magnesium, from the result of cyclic voltammogram and electrode surface analysis, by preparation of an electrolytic solution wherein a magnesium bromide (II) is dissolved in 2-methyltetrahydrofuran in order to enhance safety of the electrolytic solution.